The present invention relates generally to internal combustion engines, and more particularly to start control apparatuses for controlling the starting operation of internal combustion engines.
It becomes increasingly important to enhance the startability of internal combustion engines, because there are increasingly severe regulations for exhaust emissions at engine start, and because there is an increasing number of hybrid vehicles or vehicles equipped with an automatic engine stop function which frequently restart internal combustion engines.
Japanese Patent Application Publication No. 2002-276446 discloses a start control device for an internal combustion engine which includes a variable valve mechanism for varying at least the closing timing of intake valves, and a variable compression ratio mechanism for varying the nominal compression ratio of the internal combustion engine. The variable valve mechanism includes a valve event and lift control mechanism for continuously varying (expanding or contracting) the lift degree (defined by the lift height and operating angle) of the intake valves, and a valve lift phase control mechanism for continuously varying (advancing or retarding) the lift central phase (the central phase of the valve operating angle). The start control device is configured to control none of the variable valve mechanism and the variable compression ratio mechanism during an initial stage of the cranking operation of the internal combustion engine. For example, the start control device holds the valve lift degree constant during the initial stage of the cranking operation. After the engine speed increases due to the cranking operation, the start control device retards the valve lift central phase so that the intake valve closing timing approaches bottom dead center, thereby increasing the effective compression ratio so as to increase the intake air temperature. This is intended for enhancing the flammability in the cylinder at engine start, and quickly completing the starting operation of the internal combustion engine.